Electrical sound reproduction



March 23, 1943. MC. BATSEL ELECTRICAL souun REPRODUCTION Filed Oct. 31, 1939 attorney extended source.

Patented Mar. 23, 1943 ELECTRICAL SOUND mzraonucrron Max 0. Batsel, Haddonfield, N. 1., assignor to Radio Corporation of America, a. corporation of Delaware Application October 31, 1939, Serial No. 302,197

2 Claims. ((71. 179-1003) This invention relates to the electrical reproduction of sound and is particularly adapted to the photoelectric reproduction of sound from film in large auditoriums, although it may be usedin conjunction with other types of sound records and other locations.

The invention involves the provision of a single speaker for the reproduction of speech or similar sounds which are satisfactorily reproducible from a localized source and the provision of additional speakers over an extended area for the reproduction of music and other sound effects, the reproduction of which appears more natural from an The changev from a single speaker to the multiple speakers is .accomplished by means of an appropriate control track or the like synchronized with the sound record from which the sound is reproduced.

It has heretofore been customary,-pa'rticularly in the reproduction of sound motion pictures, to reproduce all the sound either through a single speaker or through a group of speakers, both speech and music being treated alike. If speech is reproduced through a group of speakers and particularly if they are separated by appreciable from a localized source, and in order to produce.

the proper illusion of an extended source, should be reproduced by an extended group of speakers.

In the performanceof the present invention, I provide a single speaker or small group of speakers, preferably located centrall of the I stage, for speech and I provide other speakers laterally spaced therefrom for the reproduction of music. The apparatus is so arranged that the additional speakers are normally silent, but when music is to be reproduced the additional speakers,-

together with appropriate amplifying apparatus,

are turned on, giving the effect of an extended source and, if desired, producing a slightly higher volume level.

One object of the invention is to provide an improved sound reproducing system.

Another object of the invention is to provide an improved sound reproducing system which will reproduce 'eitlier speech or music to the best effect.

Another object of the invention is to provide an improved sound reproducing system which will reproduce speech from a localized source and which will reproduce music from an extended source.

Another object of the invention is to provide an improved sound reproducing system which, in cooperation with a sound record and a control record, will reproduce sounds ither from a localized-source or from an extended source.

Another object of the invention is to provide an improved sound reproducing system which, in

cooperation with a sound record and a control.

record, will reproduce sounds either from a localized source or from an extended source, but in cooperation with a sound record without the con- -trol record will reproduce sounds only from a localized source. i

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing, in which Figure 1 is a schematic diagram of my improved sound reproducing system,

Figure 2 is a schematic diagram of an alternative switching mechanism which may be used in the apparatus of Fig. 1, and

Figure 3 is an illustration of a type of sound record and control record adapted to be used in the apparatus.

Before-describing my invention in .detail, the

type of controltrack adapted to be used therein will be briefly described.

A standard motion picture film is indicated at F in Fig. 3. This film carries the usual sound track S which is here illustrated as of the doubly modulated type with ground noise reduction. The control track is indicated at C and consists of an exposed portion over the sprocket hole area, whichexposed portion may be of greater or less width. with film running at the standard speed sprocket holes, .but the quantity of this current will besmall relative to that produced if the output can he correspondingly varied as described in the application of Charles M. .Burrlll. Serial No. 181,634, filed December 24, 1937 (RCV D5098) 1 Likewise, if the phase relation between the sprocket holes and the exposed areas is varied, th 'similar control of the output may be secured as described and claimed in the application of Charles M. Burrill, Serial No. 181,635, filed December 24, 1937 (RCV 13-5100) both of which are assigned to the assignee of the present application.

Referring now to the form of the apparatus shown in Fig. l. The usual exciter lamp I is provided from which light is directed through an appropriate slit -Sl to the sound track of the film F. The slit SI, although illustrated as a mechanical slit, for the sake of simplicity may, of course, be any other usual form such as a short focus cylindrical lens or an optical slit where a reduced image of the illustrated slit is projected, on the film. The fine line of light from the slit passes through the sound track 8 of the film to the photocell The output from the photocell normally through the amplifier |2 to the speaker it which may be located, for example, in alignment with the middle of the projection screen. The amplifier l2 may be of any usual type including a sufiicient number of stages of thermionic'amplification to give sumcient voltage gain and power output for the purpose. The loudspeaker ll' likewise may.

be of any usual type.

The portion of the output from the photocell ll may pass through the primary of the transformer 28 which is here indicated as being contended area. The amplifier I! may be of similar construction to the amplifier |2. The switching unit I4 is used to turn the amplifier I! on andoff or to regulate the power input thereto. In the form of the invention shown, the relay 21, which is indicated as open, may be closed by passing current through the winding 26 thereof, causing the output from the transformer 28 to be fecllito the amplifier l5 and to the speakers It The winding 22 is actuated as follows: A second exciter lamp 2| may be provided or light may be taken from the exciter lamp I I, and this light is directed through an aperture it upon the control track C of the film I". The aperture A may, like the slit 8|, be in the formof an optical slit or the like, but a small line of light is not dinirableinthi caseandasimplemechanical aperture may be quite satisfactory. If the apere ture is too small, the signals produced by the edges of the sprocket holes at clear portions of the control track are entirely too loud and vary quite considerably, while if the aperture is fairly large, even of the same-order of size as the sprocket holes themselves, these secondary signals are relatively decreased in magnitude and the the signals produced by the difference in ton of the sprocket holes and of the filmare relatively accentuateda Light passing through the aperture A and the output from which is fed through a transformer 22 to the amplifier 22. The amplifier 22 need not be either of high fidelity nor of great power,-

as it is only necessary for it to amplify the 86 cycle impulses produced by the control track and to provide sufficient power to actuate the relay The output from this amplifier 22 is fed through an appropriate rectifier 24 which is here illustrated as a thermionic rectifier, although any other equivalent type of rectifier may be substituted. The rectified current is fed through a filter composed of an inductance 25 and capacitors. This filter is not required to produce a high degree of filtering when a relay is used, .as it is only necessary to avoid chatterin of the relay. If, however, a thermionic valve is used, the filter .should be sufilciently good to prevent the application of 96 cycle current to the input of the amplifier it. The output from the rectifier filter circuit is connected, as shown, to the winding 26 of the relay 21.

It will be apparent that when the. control track I C is clear, the output of the photocell 2| will be at a minimum. The outputof the amplifier 22 and the. current fed to the relay winding 28 will therefore likewise be at a minimum and the relay contact 21 -will remain open. If, however, the area between. the sprocket holes on the control I track 0 is blackened, the contrast between the black area and the open sprocket holes will cause the output of the photocell 2| to be at a maximum.: In this case, the current fed by the am-' II will remain inoperative.

An alternative switching arrangement is shown in Fig. 2. In this figure the entire switching mechanism shown in the box It may be bodily substituted for the switching mechanism shown off .or if there is no output therefrom, the potential from the source 30 applied through the resistor 3| and the secondary of the transformer 22 will bias the tube 29 to cut-off and there will be no input to the amplifier ii. If, however,

outsoltrack is directed 'to-a photocell 2|, the 7s a darkened portion of the control track C is passed between the light source and the photocell 2|, the output of the amplifier 22 will increase and since the rectified output from the amplifier from a record into electrical impulses, means for amplifying said impulses, localized reproducing means connected to said amplifying means for translating said impulses into sound, additional amplifying means for independently amplifying said impulses and separated reproducing means connected tosaid additional amplifying means for electric control track reproducer, an amplifier converting said impulses into sound over an extended area, means tor translating control impulses into a control current, and means actuproducer, an amplifier connected thereto and a 10 loudspeaker connected to said amplifier, a photoand rectifier connected thereto for producing a control current, a second sound amplifier, a plurality of loudspeakers connected to said second sound amplifier, and means controlled by said control current for connecting said second sound amplifier to said photoelectric reproducer, whereby said second amplifier operates only when a control track is provided.

' MAX C. BATSEL. 

